Same old mileage questions

I just acquired an '05 LLY and am disapointed with MPG. This is my first posting so bear with me. I'm sure this has been explored a lot, so I apologize for raising it again but I'm having difficulty trying to figure out what I can do with a limited budget that will give real results. I'm considering some sort of intake system, but am concerned that it won't help much. Also, I'm thinking 4" exhaust but I doubt that cat back would really do anything. I'm not wild about violating MD's emissions requirements by replacing the cat, but may have to. Would installing a larger 4" cat help or does anyone even make one?

The LLY produces on average about 2 mpg less than the LB7. I suspect programming and a more agressive EGR are the biggest reasons for the loss.

Programming changes may offer a solution. www.kennedydiesel.com offers mpg programming for the LLY. :)

Welcome to the board!

Jim

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Originally Posted by Diesel Dimwit

I just acquired an '05 LLY and am disapointed with MPG. This is my first posting so bear with me. I'm sure this has been explored a lot, so I apologize for raising it again but I'm having difficulty trying to figure out what I can do with a limited budget that will give real results. I'm considering some sort of intake system, but am concerned that it won't help much. Also, I'm thinking 4" exhaust but I doubt that cat back would really do anything. I'm not wild about violating MD's emissions requirements by replacing the cat, but may have to. Would installing a larger 4" cat help or does anyone even make one?

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What are you getting for fuel economy and under what conditions? On my LB7, I replace the exhaust with a 4" unit, installed a performance intake, a performance program (Edge w/Attitude Monitor) and a BD left side exhaust manifold. Cost: $2000. Mileage gain: 1mpg. The power? Different story, this was a measurable improvement. So, depending on what you are trying to accomplish, don't spend more money than you are going to get back. I think it is safe to say that the exhaust and intake need to be done together, and I would not expect any mileage gains, though some would differ with me. The tuning with the programmer, or having John Kennedy tweak your computer will probably get you the best bang for the buck on mileage. The display on the dash helps me control my driving habits. Drive by wire systems don't have a very good feel to them, and my monitor tells me exactly how hard I am pushing it, thus helping me to drive more conservatively, particularly around town.

If you are towing a fifth wheel, see my posts on the trailer towing forum regarding a wind deflector.

Take a look at the gas mileage polls under Duramax 6600 forum to do a comparison to what you are getting. It does seem that some just do better than others, without much of an explanation as to why.

Thanks for the responses. Empty truck highway is about 17 mpg, while towing 7000 lb 5th is about 11. Actually, this is probably not out of line with what other LLY owners are experiencing, but achieving better would be good:). I've talked to Kennedy about his programs which are probably worthwhile but currently out of budget. I'm in the process of installing EGT & boost gauges, then will likely make some intake/exhaust mods. Then we'll see about tunes. I suspect intake/exhaust will give modest power gain but no improvement in MPG. Maybe coupled with a tune, the added power may enable me to drive with a lighter foot. I am considering a wind deflector also. I welcome any other suggestions.

Try using tow/haul mode all the time, and learn to let the transmission do your braking for you. Give it one month, averaging your mileage and gallons burned. Calculate your savings.

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Originally Posted by Mark Rinker

Try using tow/haul mode all the time, and learn to let the transmission do your braking for you. Give it one month, averaging your mileage and gallons burned. Calculate your savings.

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Mark, do you ever have trouble with tow/haul downshifting the motor and running the revs up over the redline? I had it happen just once, coming down the canyon (6% grade) while pulling my trailer, and it scared me half to death. Since then I have been nervous about the extra engine braking provided by tow/haul. I'd like to hear your experience.

Been there, done that. Many times. Notice how the later models don't even have a redline on the tach? The computer won't let you over-rev the engine, on power or compression. The early models with the redline on the tach, actually have 2 redlines. One for power, and one for compression. Obviously, you can't get too high when on power, as the 'puter pulls fuel before you hit the ceiling. It will also protect it during grade braking. If it gets too high, it'll upshift. The shaded area of the redline represents the grade braking range. Many folks brought the same question to GM, with the same concerns. I guess they got tired of explaining it, so they stopped painting the redline altogether. As long as the electronics are healthy, the engine will not let it hurt itself. But, if it finds another source of uncontrolled fuel (like the PCV or blown turbo seal), it can run away. If that happens, there's little to nothing you can do, anyway.

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Originally Posted by Mark Rinker

Try using tow/haul mode all the time, and learn to let the transmission do your braking for you. Give it one month, averaging your mileage and gallons burned. Calculate your savings.

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How do you enter this mode? Is it as simple as pressing the button on the end of the shift lever?

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Originally Posted by jjcsnlynn

How do you enter this mode? Is it as simple as pressing the button on the end of the shift lever?

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Yes, and, the T/H lamp should show on the instrument panel.

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Originally Posted by Philsauto

Mark, do you ever have trouble with tow/haul downshifting the motor and running the revs up over the redline? I had it happen just once, coming down the canyon (6% grade) while pulling my trailer, and it scared me half to death. Since then I have been nervous about the extra engine braking provided by tow/haul. I'd like to hear your experience.

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Sorry for the sloooooooooooow response, I haven't been on as often lately.

I have more miles on in tow/haul mode than not, so am very used to its shifts. Can't say as I've seen the redline/overrev issue, but normally when in the mountains and loaded with oversize boat - my ground speed is alot less than those with campers and such.

As Dmax says, with a healthy system the engine management system will kick in, so LET 'ER BUCK.

:p